In the design of many hydraulic dampers a protective tube protects the piston rod from damage while it is sliding within the piston rod guide and prevents dust or other kinds of debris from being deposited onto the piston rod surface as these debris might in turn damage the piston rod guide leading to damper leakage. In order to provide space for the compressed protective tube during the damper compression stroke its end must be attached to the damper at a certain distance from the piston rod guide. It has been known to snap an axial end of the protective tube into an annular groove machined in the wall of the damper tube or in a sleeve fixed in such a groove to accomplish this need. Such a solution, however, may not be applied to thin walled damper tubes as it would substantially decrease the durability and mechanical properties of the damper tube.
It is also known to use tubular protective plastic caps having a first axial end attached to the piston rod guide and a second axial end providing locking for the end of the protective tube. Such caps must obviously feature a sufficient axial stiffness and high critical load buckling properties to maintain their position on the damper while withstanding forces transmitted by the expanding or contracting protective tube. If these features were not present the caps would themselves scratch and damage the surface of the damper tube, which is usually covered by some anti-corrosive paint.
Patent application DE10122796 discloses a vibration damper with a corrugated protective tube surrounding the piston rod and attached at its first axial end to a stop buffer and at its second axial end to a relatively short, solid protective cap. The stop buffer, the protective tube and the protective cap form a preassembled unit and the protective cap is provided with a radially elastic edge to facilitate its connection to the protective tube. Such a radially elastic edge may be achieved by providing the cap with axially extending slots dividing the edge into individual segments. A similar short protective cap is also disclosed in the patent application DE9109020. The slots over the edge of the cap also form a number of annular openings between the damper tube and the protective tube to allow for air flow in or out of the closed space in the protective tube during its expansion or contraction, respectively.
It is one object of the present invention to provide a hydraulic damper with a protective cap of a substantial length thereby providing sufficient space for the contracted protective tube, which also has a simple and cost efficient construction, as well as improved axial and torsional stiffness and high critical load buckling properties.